International Symposium of the Health-Related Water Microbiology Group edition:15 location:Naxos, Greece date:31 May - 5 June 2009

Abstract:

Legionnaires’ disease is a sporadic or endemic disease caused by legionellae, which are Gram-negative bacteria that are ubiquitous inhabitants of aquatic environments. Out of more than 50 Legionella species, Legionella pneumophila, and more in particular L. pneumophila serogroup (sg) 1, is reported as the most common cause of legionellosis. Nevertheless, other serogroups and other Legionella species are increasingly associated with human disease, including L. dumoffii, L. micdadei, L. longbeachae and L. feeleii. Consequently, in order to minimize health risks it is important to detect not only L. pneumophila, but also other Legionella species. Furthermore, correct identification of the species is relevant for epidemiological studies and for the identification of sources of infection. Accurate detection and identification of Legionella using conventional methods is complicated by their growth requirements, their ability to enter a viable non-culturable state, their association with protozoan hosts and the occurrence of Legionella within biofilms. These drawbacks can be circumvented by molecular detection methods, especially by those based on the detection of nucleic acids. Currently, polymerase chain reaction (PCR)-based DNA array technology is one of the most suitable techniques to detect multiple organisms in a single assay, even if they differ in only a single to a few bases in the nucleotide sequence that is targeted. As a result, DNA arrays have become highly attractive for several applications.
Recently we developed a macrophage infectivity potentiator (mip) gene-based DNA array for the simultaneous detection and identification of a comprehensive set of Legionella species, including all species associated with human disease (about 20 species), and one of its protozoan hosts, Hartmanella vermiformis. Each diagnosis can be achieved within 36 hours of sampling based on an objective technique utilizing an array of specific DNA fragments. To validate the DNA array, environmental samples out of water distribution systems were collected from different companies/buildings and analyzed with both classical techniques and the developed DNA array. Although results from the DNA array were generally corroborated by the more classical techniques, the DNA array enables a more rapid, sensitive and more specific Legionella detection in the water samples. Moreover, taking into account the unlimited expanding possibilities of DNA arrays to include detector oligonucleotides for other and more microorganisms as well as for other biomarkers, this technique has the potential for studying population dynamics and ecology of several target populations in a single assay.
To our knowledge, this is the first study that emphasizes multiplex detection and identification of several Legionella species and their associated hosts, revealing essential information for legionellosis risk assessment in one single assay.